Central (visceral) obesity contributes to an excess risk of diabetes, dyslipidemia, and death from coronary heart disease in women. Women typically express central obesity during menopause but the mechanisms causing this change in fat distribution are poorly understood. Preliminary data presented here support a role for estrogen regulation of the hypothalamic-pituitary-adrenal (HPA) axis in the expression of visceral obesity in postmenopausal women. The first aim of this grant is to complete a pilot study and to test the ability of estrogen to decrease HPA activity and cortisol levels on a prospective basis in postmenopausal women. These studies will provide pilot data for studies of estrogen regulation of the HPA axis activity and subsequent changes in body fat distribution in women transitioning through the menopause. In addition, evidence indicates subjects with central (visceral) obesity have ectopic triglyceride deposition in muscle and fat, and that this deposition plays an etiological role in insulin resistance in these tissues. Magnetic resonance spectroscopy (MRS) is a novel, noninvasive imaging technique used to quantify intramyocellular (IMCL) and intrahepatic fat (IHF) and has been increasingly used in human studies of glucose metabolism. This technique therefore offers a unique opportunity to prospectively test mechanisms that might result in ectopic fat deposition. As part of my current K23, I am testing whether cortisol replacement across a normal physiological range increases visceral fat mass and insulin resistance, independent of changes in total body weight, in subjects with complete adrenal failure. To test whether increased cortisol secretion may commonly promote central obesity and ectopic triglyceride deposition, in my second and third aims I propose to establish MRS protocols measuring IMCL and IHF in humans and to apply this technique to this prospective cortisol dosing study. Funding from this R03 will build on the data I have generated to date for use in future grant applications. By providing salary support for a coinvestigator with expertise in MRS methods and a research study coordinator for subject recruitment and scheduling, this award will help me to maintain productivity and establish independence.